RECORD RAIN

Evening Post, Volume CX, Issue 44, 20 August 1930, Page 3

RECORD RAIN

THE FLOOD OF 1924

HAWKES BAY DELUGE

CAUSES ANALYSED

. On 11th March, 1924/ occurred torrential flood rains in parts of Hawkes Bay —rain the severity of whioh has probably never been equalled in any part of New Zealand since the advent of the White man. As 20 inches of rain or more fell in some places in a few hours, the rain was certainly abnormal, and it is small wonder that rivers rose rapidly, washed away bridges and roads, and drowned stock. One man was drowned and a child was killed by the collapse of a house. The total loss of stock was heavy, but a flood warning issued by the Meteorological Office enabled many to save their flocks. .

In the "New Zealand Journal of Science and Technology," Dr. E. Kiason, Director of Meteorological Services, analyses the causes and effects of this unwonted deluge. The rain, ho says, was associated with the passage of a rather deep ' cyclonic depression across tho Auckland Peninsula. "On the morning of the 10th the cyclone was centred just west of Auckland, and the pressure at its centre ,was below 29.4 in. A.n intense anticyclone over south-east-ern Australia increased the pressure gradient in the rear of the jyelone across the Tasman Sea. The centre of tho storm crossed the Auckland Peninsula during the night of the 10th, and by 9 a.m. on the 11th it was situated east, of the Bay of Islands. By the following day it had disappeared to the eastward.

"Storms of this type, and'which follow a similar track, usually bring heavy rains to the North Island, especially the Auckland, Thames, Bay of Plenty, Gisborne, and East Cape districts. Bain is a normal feature of the part of the cyclone which traversed these districts, and is caused by cold air from the southeast and south forcing up warm air brought from the north by the currents in the northern quadrant of the cyclone. But on the east coast the'rains are made much heavier owing to winds being forced to ascend the mountain ranges. Nevertheless, there must have been some very special circumstances leading to the phenomenal rains of the 11th March. The numerous and prolonged thunderstorms associated with the cyclone would point to the air being in an unusually unstable condition. It seems possible,, also, that a large mass of warm air associated with the forward part «f the'cyclone was trapped in Hawkes Bay between the mountains and the sea and surrounded on the morning of the 11th by cold air. The topography.and the wind directions would be favourable to such a development, and temperatures were very high on the morning of the 10th "at* Napier, Gisborne, and East Cape. The winds were easterly on the 10th and southerly on tho morning <of the 11th. It was noteworthy, also, that the wind at Napier on the morning of the 11th was light, whereas there were strong winds to the south. It is quite possible that a strong southerly passed up the coast and across the mouthTof "the Bay, cutting off .the warm air to_theiw"estward. This, state of things- could not last, and the warm air would soon be undermined by the cold. At the same time, cold air would have been brought up the western side of the ranges. _ If these' conjectures are correct, a situation conducive to violent convection on a large scale -would have been set up, and the resulting, rainfall would be explained.'" EAIN IN QUANTITY. Little rain, Dr. Kidson points out, had fallen anywhere before the early morning of the 11th, and in many places none at all. The great bulk fell between 4 a.m. and 6 p.m. on the 11th. The»thunderstorms were particularly vigorous at some places. The fall of rain appears to have'been heaviest in the neighbourhood "of Mr. W. G. Moore's station at -Biverbank, Kissington, the altitude of which is just over 400 feet. Mr. Moore's description of the phenomenon is quoted in full:—

"The weather had been, dry for some time, and that morning it was cloudy with a north-west breeze blowing and thunder near at hand. We had a sharp shower at 7.3o,.which:lasted an hour. It: eased off to light rain at 8.30 for about teu" minutes, and then the real storm broke.. We had to shout-to make each other heard in the house, the noise of the rain on the.iron roof being so terrific. It thundered hard nearly/all day, although not directly overhead all the time. That heavy burst kept on until about 12 o'clock1/but:at"ll.4s we thought we "had better ease the gauge a bit, so took 9in out of the bottle. (It had been taken at 9 a.m.) Prom 12 until about 2 the rain was much easier, although still veryheavy indeed. At 2 jit came on again as heavily as ever, and poured until about 3.30, when it began gradually to ease off, and finally cleared about 5.30.

"We live on a. terrace 160 ft above the Mangaone Biver, an<J can see the river from the garden. The river was normal at "7.30 a.m., and at 11.15 a.m. it took away the Kissington Bridge, which was supposed to be 34ft above ordinary summer level. At 9.30 a.m. here the river was as high as I had ever seen it "up to then, and at 10.30 it had gone over the marks of the 1897 flood by about sft. We came here in 1901, and the marks of the big flood of 1897 were then quite fresh,-and there are still places where tops of buried posts are showing through the silt, which give one a good idea of its height. "One private gauge about two miles and a half east of us registeied just over 18in on 11th March, and another one about eight miles north-north-west registered just over 16in, so that we apparently got the centre." Dr. Eidson notes that Mr. Moore's observation of a light north-westerly wind in the early morning ig support of the suggestion made as to the cause of the downpour. The rapid rise in the rivefs, frequently to heights higher than ever before recorded, naturally caused great damage, and large tracts of land were quickly inundated. Dr. Kidson briefly reviews all the effects of the downpour, and very succinctly summarises what the newspapers of the following days naturally recorded in full, both in word and in picture. The1 weather charts, maps, and diagrams with which the text is illustrated make the narrative clear to meteorologist and layman alike.